Prior art projectiles for gun ammunition have been manufactured from a generally cup-shaped metal jacket having a closed end and an open end. Heretofore, solid metal or powder-based core or cores have been inserted into metal jackets and thereafter formed into projectiles. Powder-based cores commonly comprise a mixture of metal powders which are pressed into self-supporting compacts suitable for insertion into a jacket. Some such powder-based cores exhibit little or not material porosity. Alloys of multiple metals commonly are formed into solid cores of no material porosity.
The prior art metal jackets commonly are manufactured by drawing a strip of metal into the cup-shaped jacket. In these operations, the wall thickness adjacent the closed end of the finished jacket is thicker than the thickness of the side wall of the jacket, hence the inner diameter of the jacket is maximum adjacent the open end of the jacket and tapers to a minimum value adjacent the closed end of the jacket. In most such jackets, the tapering of the inner diameter of the jacket commences pronounceable about two-thirds of the distance from the open end of the jacket and continues to the closed end of the jacket.
In a jacket having a tapering inner wall diameter, insertion of a core of the prior art which is formed outside the jacket, into the jacket becomes a problem. Specifically, if the core is of a straight cylindrical geometry, as is true of prior art cores which are formed outside the jacket, and if the diameter of the core is chosen to be almost equal to the minimum diameter of the jacket so that the core can be inserted into the jacket to the extent that one end of the core will fill the closed end of the jacket interiorly of the jacket, major problems arise.
Specifically, if the circumferential rim of the end of the cylindrical core engages the inner circumference of the jacket before the core is fully seated within the jacket, there is formed a substantially air-tight seal between the rim of the core and the inner circumference of the jacket, trapping air between the inner end of the core and the closed end of the jacket. Further insertion of the core into the jacket develops pressurized air pockets within the jacket and frequently results in actual ejection of the core from the jacket over time.
On the other hand, if the maximum diameter of the core is chosen to approximately equal the minimum inner diameter of the jacket, this design leaves a substantial annular void between the core and inner wall of the jacket at a location between the open end of the jacket and that point along the inner wall of the jacket where the actual outer diameter of the core and the inner diameter of the jacket are substantially equal. Such voids produce impressible instability of the core within the jacket, among other things.
Still further, if the core is chosen to be of a diameter equal to the minimum inner wall diameter of the jacket at a location about two-thirds of the distance from the open end of the wall in the direction of the closed end of the jacket, the length of the core will result in a substantial portion of the length of the core projecting out of the jacket at the open end of the jacket. This core must then be “seated” by pushing it further into the jacket, commonly employing a punch and die operation. This procedure effects such deformity of the core and/or jacket as to permit the core to fill the jacket volume adjacent the closed end of the jacket. In the case of solid metal cores, this action deforms the metal to cause it to fill the closed end of the jacket. As noted, this action commonly develops impressible pressurized air pockets within the jacket adjacent the closed end thereof. In the case of powder-based cores wherein the core is frangible, as opposed to skittered cores, cores formed from metal alloys, and cores wherein one of the metal powders acts as a binder for the second metal powder, the seating of a core into the closed end of a jacket literally crushes a portion of the core so that the core must be “reformed” in the crushed area by the application of relatively high forming pressure being applied in the seating operation.
Further, once the core has been seated into the jacket, the open end of the core/jacket combination must be die formed to define an give on the leading end of the core/jacket combination to thereby complete the projectile.